Grease compositions

ABSTRACT

Stable grease compositions for use with equipment at extremely low temperatures, the greases consisting of about 64.1 to 69.4 weight percent bis(2-ethylhexyl) sebacate, the balance being tetrafluoroethylene polymer having a molecular weight of 10,00050,000, a softening point of 321.1* C., a particle size less than 30 microns in diameter, and supplied as a 7.5 percent suspension in trichlorotrifluoroethane.

D United States Patent [15] 3,639,241 Messina et al. Feb. 1, 1972 [54]GREASE COMPOSITIONS 3,262,879 7/1966 Messina ..252/58 [72] Inventors:Joseph Messina Havenown; Henry 3,453,210 7/1969 Wright ..2S2/58 Gisser,Philadelphia, both of Pa.

Primary Exammer-Damel E. Wyman [73] Assignee: The United States ofAmerica as Assistant E i -L Vaughn represented by secretary of the ArmyAtt0rneyHarry M, Saragovitz, Edward .1. Kelly, Herbert Ber] [22 Filed:Sep1.26, 1969 Dubmfi [21] App]. No.: 861,486 [57] ABSTRACT Stable greasecompositions for use with equipment at ex- [52] US. Cl ..252/54.6treme'y low temperatures, the greases consisting f about 4 1 2; "Clom7lzsglom 7/24 to 69.4 weight percent bis( Z-ethylhexyl) sebacate, thebalance 1e 0 are being tetrafluoroethylene p y having a molecular 5 61References Cited of 10,000-50,000, a softening pomt of 321.1 C., aparticle size less than 30 microns in diameter, and supplied as a 7.5percent suspension in trichlorotrifluoroethane.

2 Claims, No Drawings GREASE COMPOSITIONS The invention described hereinmay be manufactured, used, and licensed by or for the Government forgovernmental purpose without the payment to us of any royalty thereon.

This invention relates to improved lubricants and more particularlyconcerns grease compositions which are chemically and physically stableover wide temperature ranges for extended periods.

Current grease-type lubricants are generally inoperable over a widetemperature range, especially at extremely low temperatures, and arethus not completely suitable for many potential military applications.For example, where lubricants do not possess physical characteristicswhich will permit their successful and reliable operation on equipmentat extremely low temperatures, serious operational problems areintroduced which often necessitates the use of auxiliary heaters toraise ambient temperatures. Similarly, extreme pressure properties ingrease compositions are usually obtained through the addition of extremepressure additives which may undesirably affect stability and viscosityproperties, among others.

It is therefore an object of the invention to provide improved greasecompositions which are free of the above-mentioned disadvantages.

Another object of the invention is to provide grease compositions whichexhibit excellent low torque characteristics at extremely lowtemperatures, good shear and oxidation stability, a low fluid separationand high dropping point, and good extreme pressure properties.

Other objects and features of the invention could become apparent as theinvention is more fully hereinafter disclosed.

Briefly, we have discovered new grease compositions especially useful tothe military wherein an ester of a carboxylic acid, i.e.,bis(2-ethylhexy1) sebacate is thickened with a perfluoro polymer.

More specifically, we have discovered that bis(2-ethylhexyl) sebacatemay be thickened with tetrafluoroethylene polymer (hereinafter referredto as PTFE) having a molecular weight of about l0,000-50,000 to producea stable, greasetype lubricant for military applications, among others.

Typical properties of the PTFE solids used in the preparation of ourinventive compositions are:

a softening point of 32 l 1 C.,

a particle size under 30 microns in diameter, the PTFE solids beingsupplied as a 7.5 percent suspension in trichlorotrifluoroethane. Theviscosity of the base fluid, determined at 37.78 C. is l2.7 centistokes.

The greases were prepared as follows:

The dispersion of PTFE in trichlorotrifluoroethane was heated on a steambath until 50-75 percent of the solvent evaporated. Approximately 75percent of the required quantity of bis(2-ethylhexyl) sebacate was thenadded, the mixture was stirred and heating continued until all thetrichlorotrifluoroethane had evaporated. The trichlorotrifluoroethanewas analyzed by gas chromatography using the following technique. Asample of the grease mixture was eluted using C.P. benzene. The elutedfluid mixture was placed in a gas chromatograph with a feet carbowax 20M column at 50 C. and a helium gas flow of IO ml. per minute. Absence ofa retention peak after 3.3 minutes indicated that all of thetrichlorotrifluoroethane had evaporated. The remainder of thebis(2-ethylhexyl) sebacate was then added while stirring, and stirringcontinued until a homogeneous greaselike product was obtained. Themixture was cooled to room temperature and passed through a colloid millwith the stator-to-rotor clearance set at 0.001 in. The homogenizedmixture was then placed in a freezer at minus 10 C. for 24 hours,removed and permitted to remain at room temperature an additional 24hours prior to use. At least 2 batches of each grease were prepared. Thethickener content was determined in duplicate on each batch using aSoxhlet extractor and benzene. The data are presented in table I below:

TABLE I Grease Composition The PTFE thickener content above represents aminimum concentration necessary to provide a stable greaselikestructure. If less than the amount above: is used, a semifluidconsistency usually results. The effective range of base fluid is about64.] to 69.4 weight percent.

Shear stability tests were conducted using the one-quarter scale (ASTM D1403-62) grease worker modified topermit automatic operationaln table IIbelow, the values representing double strokes, the maximum change inconsistency is 71 units (1 unit=one-tenth of a millimeter). After 6months storage, the change in worked consistency on the stored sampleswas not significantly different than the change on the unstored samples.The table indicates that the sebacate- -PTFE thickened greases wereshear stable, and that this property would not change significantly withpassage of time. All values presented in tables I] thru Vl were obtainedon grease compositions having the specific proportions as stated intable 1 above.

TABLE II Shear Stability Strokes Grease 0* 500 l0,000 l00,000

Bis(2-ethylhexyl) sebacate 323(306) 333(3] l) 340(327) 394(354)Unworked, no strokes.

Data in parenthesis are values obtained after 6 months storage.

TABLE III Fluid Separation And Dropping Point Bleeding, Dropping G easewt, 7! Point, C.

Bis(2-ethylhexyl) sebacate 4.2 254.5

Fed. Std. Test Method 321.2 (Fed. Std. Test Method 791b, 1966), I00" C.for 30 hours.

"ASTM D 2265-67.

Our greases exhibited a high dropping point (temperature at which thefirst drop of material falls from the cup), a property useful forhigh-temperature applications.

in comparison therewith, prototype grease composition used currently byall military services of the United States Government, other than forchassis lubrication, is a diester mixture base grease includingadditives and lithium hydroxystearate, MlLG-23827A, Aug. 1, 1965,yielded 5.0 weight percent bleeding and a dropping point of about 163C., considerably inferior to our grease composition.

The Four-Ball EP Tester determines loads at incipient seizure and atweld. Incipient seizure is defined as the load at which a suddensizeable increase in wear scar diameter occurs, and weld is the load atwhich motion of the upper rotating ball in relation to the other threeis no longer possible. The data in table lV below show comparableextreme pressure properties when compared with MlL-G-23827A grease,hereinabove referred to:

TABLE IV Extreme Pressure Properties Seizure Grease loud, kg. Weld load,kg.

Bis(2-cthylhexyl) sebacate 90 200 23827A 90 [90 TABLE V OxidationStability* Grease Pressure Drop (lo/sq. in.)

Bis(2-ethylhexyl) sebacate 23827A "ASTM-D-942-50 I00 hours at I2 I .2C.

TABLE vi Torque (g.-cm.) at 53.9 C.

Grease Starting Running Bis(2-ethylhexyl) sebacate 404 I9] MlL-G-A 3825850 We wish it to be understood that we do not desire to be limited tothe exact details described, for obvious modifications will occur to aperson skilled in the art.

We claim:

1. A homogeneous grease composition comprising about 64.1 to 69.4 weightpercent bis(Z-ethylhexyl) sebacate, the balance being substantiallytetrafluoroethylene polymer having a molecular weight between about10,000 to 50,000, and a particle size less than about 30 microns indiameter.

2. A homogeneous grease composition exhibiting low torquecharacteristics at 65 F., shear and oxidation stability, low bleedingand a high dropping point, and improved extreme pressure propertiesconsisting essentially of about 69.4 weight percent bis(2-ethylhexyl)sebacate having a pour point below 65 F., and tetrafluoroethylenepolymer having a molecular weight ranging between about 10,000 to50,000, and a particle size ofless than 30 microns in diameter.

2. A homogeneous grease composition exhibiting low torquecharacteristics at -65* F., shear and oxidation stability, low bleedingand a high dropping point, and improved extreme pressure propertiesconsisting essentially of about 69.4 weight percent bis(2-ethylhexyl)sebacate having a pour point below -65* F., and tetrafluoroethylenepolymer having a molecular weight ranging between about 10,000 to50,000, and a paRticle size of less than 30 microns in diameter.